It's always been Tony, right from the start. They're soulmates, they were made for one another. Anyone can see that.
Besides, Gibbs is out of the question because Ziva said so herself, he's like a father to her. So, romantic involvement with him just wouldn't be right. And McGee is more like a close friend/brotherly type of figure to her. Plus he belongs with Abby anyway. So it's TONY all the way. :D
GIBBS! ahaha jk jk! but my REAL answer is Tony. Cuz, duh, don't it look like he's fallin' for her? They look totally good together. And, if she were with Gibbs... ew, disturbing. He's cool and all, but...*shudder* and McGee's too "brotherly" (she even said so)